Film-forming material and film

ABSTRACT

A coating material containing an oxyfluoride of yttrium and having a Fisher diameter of 1.0 to 10 μm and a tap density TD to apparent density AD ratio, TD/AD, of 1.6 to 3.5. The coating material preferably has a pore volume of pores with a diameter of 100 μm or smaller of 1.0 cm 3 /g or less as measured by mercury intrusion porosimetry. A coating containing an oxyfluoride of yttrium and having a Vickers hardness of 200 HV0.01 or higher. The coating preferably has a fracture toughness of 1.0×10 2  Pa·m 1/2  or higher.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of InternationalApplication No. PCT/JP2017/028578, filed on Aug. 7, 2017, and claimspriority to Japanese Patent Application No. 2016-215615, filed on Nov.2, 2016. The entire disclosures of the above applications are expresslyincorporated herein by reference.

BACKGROUND Technical Field

This invention relates to a coating material containing an yttriumoxyfluoride and a coating.

Related Art

A halogen gas, such as fluorine or chlorine, is sometimes used in anetching step, such as plasma etching, in the fabrication ofsemiconductor devices. In order to prevent halogen gas corrosion of anetching apparatus, the inner side of the etching apparatus is usuallycoated with a highly anti-corrosive substance. Materials containing arare earth element typified by yttrium are often used as such asubstance.

WO2016129457 discloses a coating powder containing a rare earthoxyfluoride (Ln-O—F) and having an average particle size (D₅₀) of 0.1 to10 μm, a pore volume of pores having a diameter of 10 μm or smaller of0.1 to 0.5 mL/g as measured by mercury intrusion porosimetry, and aratio of the maximum peak intensity (S0) assigned to a rare earth oxide(Ln_(x)O_(y)) in the 2θ angle range of from 20° to 40° to the maximumpeak intensity (S1) assigned to the rare earth oxyfluoride (Ln-O—F) inthe same 2θ angle range, S0/S1, of 1.0 or smaller in powder X-raydiffractometry using Cu-Kα rays or Cu-Kα1 rays. WO2016129457 teachescoating formation using the powder as a coating material by PVD(physical vapor deposition).

WO2016129457 also discloses a sintered compact as a coating materialwhich contains a rare earth oxyfluoride (Ln-O—F), teaching coatingformation using the sintered compact by PVD.

According to WO2016129457, use of the disclosed coating powder andsintered compact promises high plasma resistance. However, the demandfor semiconductor fabrication apparatus with improved resistance tocorrosion by plasma has recently been increasing. The same demandapplies to those materials containing yttrium oxyfluoride. In thisregard, a coating formed by PVD using the powder or sintered compactdescribed in WO2016129457 still leaves room for further improvement inplasma resistance than before.

SUMMARY

An object of the invention is to provide a coating material capable ofeliminating various disadvantages associated with the above mentionedconventional techniques.

As a result of extensive investigations, the inventors have found that acoating material containing an oxyfluoride of yttrium and having aspecific Fisher diameter and a specific ratio of tap density TD toapparent density AD, TD/AD, provides by PVD a coating containing theyttrium oxyfluoride and having a specific hardness and that theresultant coating is excellent in resistance to corrosion by plasma,such as fluorine-based or chlorine-based plasma, and thus completed thepresent invention.

Based on the above findings, the invention provides a coating materialcontaining an oxyfluoride of yttrium (hereinafter also called an yttriumoxyfluoride) and having a Fisher diameter of 1.0 to 10 μm and a tapdensity TD to apparent density AD ratio, TD/AD, of 1.6 to 3.5.

The invention also provides a coating containing an yttrium oxyfluorideand having a Vickers hardness of 200 HV0.01 or higher.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a powder X-ray diffractogram of the coating material obtainedin Example 1.

FIG. 2A and FIG. 2B are each a scanning electron micrograph of thecoating material obtained in Example 1.

FIG. 3 is an optical micrograph of the coating obtained in Example 1.

FIG. 4 is an optical micrograph of the coating obtained in ComparativeExample 1.

FIG. 5 is a scanning electron micrograph of a projection.

FIG. 6 is an X-ray diffractogram of the coating obtained in Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The coating material of the invention will be described on the basis ofits preferred embodiment.

The coating material of the embodiment is characterized, in one aspect,by containing an yttrium oxyfluoride. An yttrium oxyfluoride isgenerally represented by YO_(x)F_(y) (0<X, and 0<Y). The coatingmaterial of the embodiment preferably has a powder form.

YO_(x)F_(y) is a compound composed of yttrium (Y), oxygen (O), andfluorine (F). With a view to enhancing the effect in forming a hard andhighly plasma-resistant coating film, x preferably satisfies0.04≤x≤1.00, more preferably 0.10≤x≤1.00, even more preferably0.30≤x≤1.00, still more preferably 0.50≤x≤1.00. Typical examples of theYO_(x)F_(y) include Y₁O₁F₁, Y₅O₄F₇, Y₅O₆F₇, Y₇O₆F₉, Y₁₇O₁₄F₂₃, and(YO_(0.826)F_(0.17))F_(1.174). These compounds may be used eitherindividually or in combination of two or more thereof. In the followingdescription, YO_(x)F_(y) will also be expressed simply as YOF.

PVD is a process in which a coating material is evaporated or sublimatedin vacuo, and the vapor of the material reaches and deposits on asubstrate to form a coating. In order to form a hard coating, thecoating material is required to be efficient in melting and evaporationor in sublimation in the form of powder in a deposition chamber. Fromthis viewpoint, the coating material of the embodiment has a largerparticle size than conventional coating powders containing an yttriumoxyfluoride. Specifically, the coating material of the invention has aFisher diameter of at least 1.0 μm whereby the powder particles areprevented from being swept up to cause formation of projections on thesurface of the resulting coating. Having a Fisher diameter of notgreater than 10 μm, on the other hand, the coating material of theinvention melts and evaporates or sublimates at a certain or higher ratethereby enabling stable coating formation. For these considerations, theFisher diameter of the coating material is preferably 1.3 to 8 μm, morepreferably 1.5 to 6 μm. The Fisher diameter can be measured by themethod described in Examples hereinafter given.

The coating material of the embodiment is also characterized, in anotheraspect, by having a ratio of tap density TD to apparent density AD,TD/AD in a specific range. The inventors intensively studied therelation between the physical properties of a powder containing anyttrium oxyfluoride and the hardness of a coating formed therefrom byPVD. They found as a result that the TD/AD is an important factor forobtaining a hard coating. A sufficiently hard coating results when theTD/AD of the yttrium oxyfluoride-containing coating material falls in aspecific range. Having a TD/AD in a specific range is also effective inpreventing the powder particles from being swept up in a depositionchamber. Specifically, the TD/AD is preferably 1.6 to 3.5, morepreferably 1.7 to 3.2, even more preferably 1.8 to 3.0. The TD/AD can bedetermined by the method described in Examples given later.

With the view of obtaining a harder and more plasma-resistant coating,the tap density TD of the coating material of the embodiment ispreferably 1.0 to 2.0 g/cm³, more preferably 1.2 to 1.8 g/cm³.

It is preferred that the coating material of the embodiment have aspecific volume of pores of 100 μm or smaller diameter as measured bymercury porosimetry (hereinafter also simply referred to as the porevolume). The pore volume depends on not only the particle size of thecoating material but also the shape and the like of the particlesconstituting the coating material. Therefore, powders having the sameparticle size do not always have the same pore volume. Specifically, thepore volume of the coating material of the invention is preferably 1.0cm³/g or smaller. A coating material having the pore volume in thatrange provides a PVD coating which is harder and more plasma resistant.To ensure the hardness of the resulting coating, the pore volume of thecoating material of the invention is more preferably 0.9 cm³/g orsmaller, even more preferably 0.8 cm³/g or smaller. While the lowerlimit of the pore volume is not particularly specified, it is usually0.1 cm³/g or larger. The pore volume can be determined by the methoddescribed in Examples.

It is preferred that the coating material of the embodiment have anangle of repose in a specific range. A material with a larger angle ofrepose is less fluid and therefore capable of forming a coating by PVDin a more stable manner. As a result, a coating with desirable hardnessand fracture toughness and fewer projections is obtained easily. Theangle of repose of the coating material of the embodiment is preferably40° or larger, more preferably 43° or larger, even more preferably 45°or larger. There is no preferred upper limit on the angle of repose, butthe angle of repose is generally 60° or smaller. The angle of repose canbe measured by the method described in Examples.

The coating material having the specific Fisher diameter, tap density toapparent density ratio (TD/AD), pore volume, and angle of repose ispreferably prepared by the method hereinafter described.

With a view to form a coating with further improved resistance tocorrosion by plasma, the oxygen content of the coating material ispreferably 0.3 to 13 mass %, more preferably 3 to 13 mass %, even morepreferably 6 to 13 mass %. The oxygen content can be determined by themethod described in Examples.

The coating material of the embodiment shows a peak assigned to YOF whenanalyzed by X-ray diffractometry (XRD). In the analysis by XRD, it ispreferred that the X-ray diffractogram of the coating material of theembodiment be such that the main peak appearing in the 2θ angle range offrom 0° to 70° be assigned to YOF. In the XRD analysis, a diffractionpeak assigned to YF₃ may or may not be observed, but if observed, themain peak assigned to YF₃ appearing in the 2θ angle range of from 0° to70° is preferably lower than the main peak of YOF in the same 2θ anglerange. More specifically, the height of the main peak assigned to YF₃ ispreferably not more than 20% of that of the main peak assigned to YOF.In the XRD analysis, a diffraction peak assigned to Y₂O₃ may or may notbe observed in the 2θ angle range of from 0° to 70°, but if observed,the height of the main peak assigned to Y₂O₃ in that range is preferably40% or less, more preferably 30% or less, of that of the main peakassigned to YOF in that range. XRD of the coating material can beperformed according to the method described in Examples.

Coating techniques applicable to the coating material of the embodimentinclude PVD. PVD is a process in which a metal evaporant is heated intovapor. PVD may be ion plating. Ion plating is a process in whichevaporant vapor is positively charged in plasma in a reduced pressurevessel, attracted to a negatively charged substrate, and deposited onthe substrate to form a coating layer. PVD may be vacuum deposition,which is a process using no plasma. In performing PVD, an inert gas,such as argon, is introduced into a deposition chamber. In the presentembodiment ion plating is particularly preferred in terms of obtaining adense, hard, and highly plasma-resistant coating. In view of obtaining acoating with further improved plasma-resistance, ion plating ispreferably carried out under conditions of: inert gas or reactive gaspressure, 0.01 to 0.1 Pa; EB output power, 0.4 to 10 kW; and RF power,0.2 to 3.0 Kw.

A preferred method for preparing the coating material of the embodimentwill then be described. It should be understood, however, that thecoating material of the invention is by no means limited by the methodof preparation.

The preferred method for preparing the coating material of theembodiment includes step 1 in which yttrium oxide (Y₂O₃) powder andyttrium fluoride (YF₃) powder are dry blended and step 2 in which themixture obtained in step 1 is fired. Steps 1 and 2 will be described indetail.

Step 1:

The Y₂O₃ powder to be blended preferably has a BET specific surface area(S) of 1 to 30 m²/g. The YF₃ powder to be blended preferably has a BETspecific surface area (S) of 0.1 to 5 m²/g. The BET specific surfacearea (S) can be determined using an automatic surface area analyzerMacsorb® model 1201 from Mountech Co., Ltd. according to the singlepoint BET method. A nitrogen-helium mixed gas (N₂: 30 vol %) may be usedas an adsorbate.

In step 1, Y₂O₃ powder and YF₃ powder are dry blended. Dry blending maybe conducted by any means. For example, the powders may be mixed byagitation in a vessel, or a mixing machine, such as a double coneblender, a V blender, or a Henschel mixer, may be used. Incorporatingammonium fluoride (NH₄F) into the Y₂O₃/YF₃ mixed powder is recommendedbecause of enabling low-temperature firing. The mixing ratio of Y₂O₃powder, YF₃ powder, and ammonium fluoride (NH₄F) is preferably 2.6 to61.9 mass % of Y₂O₃, 36.0 to 96.2 mass % of YF₃, and 1.2 to 2.1 mass %of ammonium fluoride (NH₄F), provided that the total of them does notexceed 100 mass %.

Step 2:

The mixture obtained in step 1 is fired in step 2. The firing atmospheremay be an oxygen-containing atmosphere, such as air, or an inertatmosphere, such as argon or nitrogen gas atmosphere. Anoxygen-containing atmosphere is preferred in view of sufficientlyforming YO_(x)F_(y). The firing temperature is preferably 450° C. orhigher and lower than 750° C. Firing at a temperature in that rangeresults in more efficient production of the coating material of theinvention. The firing temperature is more preferably 500° to 700° C.,even more preferably 550° to 650° C.

The firing time is preferably 1 to 100 hours, more preferably 5 to 50hours, even more preferably 10 to 30 hours, provided that the firingtemperature is within the above range.

The thus prepared coating material is suitably used to form the coatingof the embodiment. Examples of substrates to be coated include metalssuch as aluminum, metal alloys such as aluminum alloys, ceramics such asalumina, and quartz. The substrate on which the coating is to be formedmay previously coated with an anti-corrosive coating.

The coating of the embodiment will next be described.

The coating of the embodiment is characterized, in one aspect, bycontaining an yttrium oxyfluoride represented by YO_(x)F_(y), wherein0<x and 0<y, which will also be expressed simply by YO_(x)F_(y) or moresimply by YOF. YO_(x)F_(y) is a compound composed of yttrium (Y), oxygen(O), and fluorine (F). In order for the coating to be hard and highlyplasma-resistant, x preferably satisfies 0.04≤x≤1.00, more preferably0.10≤x≤1.00, even more preferably 0.30≤x≤1.00, still more preferably0.50≤x≤1.00. Typical examples of the YO_(x)F_(y) include Y₁O₁F₁, Y₅O₄F₇,Y₅O₆F₇, Y₇O₆F₉, Y₁₇O₁₄F₂₃, and (YO_(0.826)F_(0.17))F_(1.174). Thecoating may contain either one or more of these compounds.

The coating of the embodiment contains YOF and has a Vickers hardness of200 HV0.01 or higher. With this hardness the coating exhibits excellentresistance to corrosion by plasma, such as halogen-based plasma. Such ahard coating containing YOF has been difficult to form from conventionalcoating materials. To further ensure the plasma corrosion resistance,the coating preferably has a Vickers hardness of 220 HV0.01 or higher,more preferably 250 HV0.01 or higher, even more preferably 280 HV0.01 orhigher. The coating with the Vickers hardness in that range is obtainedby processing the coating material of the embodiment by PVD. Inparticular, a hard coating is easily formed by ion plating. The Vickershardness can be measured by the method described in Examples.

In order for the coating of the embodiment to have excellent plasmaresistance, the coating preferably has, in addition to the abovespecified hardness, a fracture toughness of 1.0×10² Pa·m^(1/2) or more.For that purpose, the fracture toughness is more preferably 1.0×10³Pa·m^(1/2) or more, even more preferably 1.0×10⁴ Pa·m^(1/2) or more,still more preferably 1.0×10⁵ Pa·m¹¹² or more, yet more preferably1.0×10⁶ Pa·m¹¹² or more. The fracture toughness can be determined by themethod described in Examples. The coating with the above specifiedpreferred fracture toughness can be obtained by processing the coatingmaterial of the embodiment by PVD.

With a view to improving step coverage as well as plasma corrosionresistance, the coating of the embodiment preferably has a thickness ofat least 3 μm. With the same view, the thickness of the coating is morepreferably 5 μm or larger, even more preferably 10 μm or larger. Thereis no particular upper limit on the coating thickness. The coating withthe above specified preferred thickness can be obtained by processingthe coating material of the embodiment by PVD. The coating thickness canbe measured by the method described in Examples.

It is preferred that the number of projections per 1.0 cm×1.0 cm area ofthe coating of the embodiment be not greater than 10, more preferablynot greater than 8, even more preferably not greater than 4, still morepreferably not greater than 2. The expression “the number of projectionsper 1.0 cm×1.0 cm area” denotes the number of projections observed in a1.0 cm×1.0 cm square of a surface of a coating. Because conventionalcoating powders containing an oxyfluoride of yttrium have smallerparticle sizes and are therefore more light-weight, they are liable tobe swept up during PVD. The swept up powder particles can adhere to thecoating film being deposited, and on which particles vapor continues todeposit to form projections. If a coating having such projections isprovided in a plasma etching chamber in the semiconductor fabrication,the projections are selectively etched by plasma to cause particleshedding. In contrast, the coating of the embodiment has very fewprojections and is therefore excellent in resistance to corrosion byplasma. As used herein, the term “projection” refers to a projection onthe surface of the coating with a maximum length of 5 μm or larger. Theterm “maximum length” as used herein refers to the maximum length of theshape of a projection when viewed on its projecting side from thedirection perpendicular to the surface of the coating, i.e., the lengthof the longest of all the line segments crossing the top-view shape ofthe projection. When the top-view shape of a projection is circular, themaximum length corresponds to the diameter of the circle. The number ofprojections can be counted by the method described in Examples.

The coating of the embodiment shows an X-ray diffraction peak assignedto YOF when analyzed by XRD. In the analysis by XRD, it is preferredthat the main peak appearing in the 2θ angle range of from 0° to 70° beassigned to YOF. In the XRD analysis, a diffraction peak assigned to YF₃may or may not be observed, but if observed, the main peak assigned toYF₃ appearing in the 2θ angle range of from 0° to 70° is preferablylower than the main peak of YOF in the same 2θ angle range. Morespecifically, the height of the main peak assigned to YF₃ is preferablynot more than 20% of that of the main peak assigned to YOF. Adiffraction peak assigned to Y₂O₃ may or may not be observed in the 2θangle range of from 0° to 70°, but if observed, the height of the mainpeak assigned to Y₂O₃ in that range is preferably 40% or less, morepreferably 30% or less, of that of the main peak assigned to YOF in thatrange. XRD of the coating can be performed according to the methoddescribed in Examples.

The oxygen content of the coating is preferably 0.3 to 15 mass %, morepreferably 3 to 14 mass %, even more preferably 6 to 13 mass %. Theoxygen content can be determined by the method described in Examples.

The excellent plasma resistance being taken advantage of, the coating ofthe embodiment is used to coat the inside components of etchingequipment of a semiconductor fabrication apparatus, such as the etchingchamber wall, substrate holder, electrostatic chuck, and gas inlet, andconstituent members of these components. The coating of the embodimentis applicable to constituent members of various plasma processingsystems and chemical plants as well as the inside of a semiconductorfabrication apparatus and its constituent members. The coating of theembodiment exhibits excellent resistance to both fluorine- andchlorine-based plasma as will be demonstrated in Examples below. Thecoating of the embodiment also shows excellent resistance to plasma ofvarious gases, such as oxygen, NF₃, oxygen/NF₃, ammonia, NF₃/oxygen,nitrogen, and hydrogen, and does not substantially change in surfaceproperties during plasma etching using these gases.

EXAMPLES

The invention will now be illustrated in greater detail, but it shouldbe understood that the invention is not construed as being limitedthereto. Unless otherwise noted, all the percentages are by mass.

Example 1

Sixty-five grams of yttrium oxide (Y₂O₃) powder available from NipponYttrium Co., Ltd. (BET specific surface area S: 3.1 m²/g), 28 g ofyttrium fluoride (YF₃) powder from Nippon Yttrium Co., Ltd. (BETspecific surface area S: 0.4 m²/g), and 7 g of ammonium fluoride (NH₄F)were dry mixed. The resulting mixture was put in an alumina containerand fired in an electric oven in the atmosphere at 700° C. for 10 hoursto make a coating material of Example 1.

Example 2

Sixty-four grams of yttrium oxide (Y₂O₃) powder from Nippon Yttrium Co.,Ltd. (BET specific surface area S: 3.1 m²/g), 29 g of yttrium fluoride(YF₃) powder from Nippon Yttrium Co., Ltd. (BET specific surface area S:0.4 m²/g), and 7 g of ammonium fluoride (NH₄F) were dry mixed. Theresulting mixture was put in an alumina container and fired in anelectric oven in the atmosphere at 650° C. for 12 hours to prepare acoating material of Example 2.

Example 3

Thirty-nine grams of yttrium oxide (Y₂O₃) powder from Nippon YttriumCo., Ltd. (BET specific surface area S: 3.1 m²/g), 39 g of yttriumfluoride (YF₃) powder from Nippon Yttrium Co., Ltd. (BET specificsurface area S: 0.4 m²/g), and 12 g of ammonium fluoride (NH₄F) were drymixed. The resulting mixture was put in an alumina container and firedin an electric oven in the atmosphere at 550° C. for 16 hours to preparea coating material of Example 3.

A coating material was prepared in Comparative Example 1 below in thesame manner as in Example 9 of WO2016129457 cited above.

Comparative Example 1

Forty-seven grams of yttrium oxide (Y₂O₃) powder available from NipponYttrium Co., Ltd. (BET specific surface area S: 20 m²/g; D₅₀: 0.24 μm)and 53 g of yttrium fluoride (YF₃) powder from Nippon Yttrium Co., Ltd.(BET specific surface area S: 0.4 m²/g; D₅₀: 7.4 μm) were mixed(YF₃/Y₂O₃ molar ratio=1.74). The resulting mixture was put in an aluminadish and fired in an electric oven in the atmosphere at 950° C. for 8hours. The fired product was dry ground in an atomizer, mixed with anequal mass of pure water, and wet ground first in a bead mill using 2mm-diameter yttria-stabilized zirconia (YSZ) balls for 2 hours and thenin a bead mill using 1.2 mm-diameter YSZ balls for 0.5 hours to make awet-ground slurry. The wet-ground slurry was dried at 120° C. for 12hours to give a coating material of Comparative Example 1.

The coating materials prepared in Examples 1 to 3 and ComparativeExample 1 were analyzed based on the following properties 1 to 5.

1. Fisher Diameter (μm)

Fisher diameter (μm) was measured using Fisher Model 95 Sub-Sieve Sizerfrom Fisher Scientific in accordance with JIS H2116.

2. TD/AD

Tap density TD (g/cc) and apparent density AD (g/cc) were measured usinga multi-functional powder properties measuring instrument Multi-TesterMT-1001k (from Seishin Enterprise Co., Ltd.) in accordance with JISZ2512 and JIS K5101, respectively. The TD to AD ratio was calculatedfrom the measurements.

3. Pore Volume

Pore volume was measured using AutoPore IV from Micromeritics inaccordance with JIS R1655.

4. Angle of Repose

Angle of repose was measured using a multi-functional powder propertiesmeasuring instrument Multi-Tester MT-1001k (from Seishin Enterprise Co.,Ltd.) in accordance with JIS R9301.

5. Oxygen Content

Oxygen content was measured by the inert gas fusion method using anoxygen/nitrogen analyzer EMGA-920 from Horiba, Ltd.

The results of the measurements of the properties 1 to 4 are shown inTable 1.

TABLE 1 Fisher Pore Angle of Diameter TD AD Volume Repose (μm) (g/cm³)(g/cm³) TD/AD (cm³/g) (°) Example 1 3.0 1.48 0.58 2.55 0.51 50 Example 22.7 1.43 0.62 2.31 0.60 47 Example 3 4.8 1.55 0.63 2.46 0.55 46 Compara.0.9 1.15 0.73 1.57 0.33 37 Example 1

The oxygen content of the coating materials of Examples 1, 2, and 3 asmeasured by the method 5 described above were 12%, 9%, and 6%,respectively. The oxygen content of the coating material of ComparativeExample 1 measured by the same method was 10%. The coating materials ofExamples were analyzed by powder XRD under the conditions below. As aresult, the main peak observed in the 2θ angle range of from 0° to 70°was assigned to YOF in every Example. The height of the main peakassigned to YF₃ in the 2θ angle range of from 0° to 70° was 20% or lessof that of the main peak assigned to YOF in the same 2θ angle range inevery Example. The height of the main peak assigned to Y₂O₃ in the 2θangle range of from 0° to 70° was 40% or less of that of the main peakassigned to YOF in the same 2θ angle range in each Example. The X-raydiffractogram of the coating material of Example 1 is shown in FIG. 1.

Method for Measuring X-Ray Diffraction:

Equipment: Ultima IV (from Rigaku Corp.)

Source: CuKα rays

Tube voltage: 40 kV

Tube current: 40 mA

Scanning speed: 2°/min

Step size: 0.02°

Measurement range: 20=0° to 70°

The coating material of Example 1 was observed using an SEM. The SEMimages are shown in FIGS. 2A and 2B.

A coating was produced by the following method using each of the coatingmaterials of Examples 1 to 3 and Comparative Example 1. The coatingsformed of the coating materials of Examples 1 to 3 and ComparativeExample 1 will be called the coating of Examples 1 to 3 and ComparativeExample 1, respectively.

Production of Coating:

A 100 mm-side square alumina ceramic plate (thickness: 2 mm) wasprepared as a substrate. A coating was formed on the substrate by ionplating under conditions: argon gas pressure, 0.04 Pa; EB output power,4.0 kW; and RF output power, 2.0 kW.

The coatings of Examples 1 to 3 and Comparative Example 1 were examinedfor the following properties 6 to 10.

6. Vickers Hardness and Fracture Toughness

Vickers hardness was measured in accordance with JIS Z2244 using atester HM-220 from Mitsutoyo Corp. A sample on the tester was indentedwith a diamond pyramid indenter with a 136° angle between opposite facesby applying a test force of 0.01 kgf for 10 seconds in the atmosphere at25° C. to leave an indentation on the surface of the sample. Thehardness is calculated on the basis of the area of the indentation.

Fracture toughness was obtained in accordance with JIS R1607. The lengthof the cracks propagated from the corners of the indentation formed inthe Vickers hardness measurement was measured using a scanning electronmicrograph. The fracture toughness value was calculated from thefollowing equation, in which the applied load was 1.96×10⁻⁴ N, and theelasticity modulus was 1.8×10¹¹ Pa.

Fracture toughness=0.018×(E/HV)^(1/2)(P/C ^(3/2))

where E, elasticity modulus (Pa); HV, Vickers hardness (Pa); P, appliedload (N); C, half of average crack length (m).

The Vickers hardness was calculated according to equation:

HV=1.8544×P/(2a)²

where a is half of diagonal length of indentation (m).

Vickers hardness measurement and fracture toughness measurement weretaken at three points, and the averages of the measurements wereobtained.

7. Coating Thickness

Coating thickness was measured using Surfcom from Tokyo Seimitsu.

8. Number of Projections

Projections with a maximum length of 5 μm or greater were counted over a1.0 cm×1.0 cm area of the coating using an optical microscope (×250).Count was taken at three different areas, and the results were averaged.The optical micrograph of the coating of Example 1 is shown in FIG. 3,and that of Comparative Example 1 is shown in FIG. 4. The projectionsare displayed as white spots in, e.g., FIG. 4. An SEM image of one ofthe projections is shown in FIG. 5. The projection shown in FIG. 5 has agenerally elliptical top-view shape.

The results of the above measurements are shown in Table 2.

TABLE 2 Vickers Fracture Hardness Toughness Coating Number of (HV0.01)(Pa · m^(1/2)) Thickness (μm) Projections Example 1 284.3 5.7 × 10⁶ 15 2Example 2 382.4 3.7 × 10³ 15 4 Example 3 441.2 8.5 × 10² 15 7Comparative 196.2 0.9 × 10² 15 198 Example 1

9. XRD

The coating was analyzed by XRD under the following conditions. In everyExample, the main peak observed in the 2θ angle range of from 0° to 70°was assigned to YOF, the height of the main peak assigned to YF₃observed in that 2θ angle range was 20% or less of that of the main peakassigned to YOF in the same 2θ angle range, and the height of the mainpeak assigned to Y₂O₃ in that 2θ angle range was 40% or less of that ofthe main peak assigned to YOF in the same 2θ angle range. The X-raydiffractogram of the coating of Example 1 is shown in FIG. 6.

Conditions of XRD:

Equipment: Ultima IV (from Rigaku Corp.)Source: CuKα raysTube voltage: 40 kVTube current: 40 mAScanning speed: 2°/minStep size: 0.02°Measurement range: 2θ=0° to 70°

10. Oxygen Content of Coating

The oxygen content of the coating was measured by the inert gas fusionmethod using an oxygen/nitrogen analyzer EMGA-920 from Horiba, Ltd.

The oxygen contents of the coatings of Examples 1, 2, and 3 were foundto be 13%, 10%, and 7%, respectively. The oxygen content of the coatingof Comparative Example 1 was 18%.

Resistance to Corrosion by Halogen-Based Plasma:

The coatings obtained in Examples and Comparative Example were evaluatedfor resistance to corrosion by halogen plasma by the method below. Theresults obtained are shown in Table 3.

Method for Evaluating Resistance to Particle Shedding:

The coating formed on a 100 mm square aluminum ceramic substrate wassubjected to plasma etching. A 3-in. diameter silicon wafer was placedin the chamber beforehand. The number of particles having a particlesize of about 0.1 μm or greater out of those shed from the coating dueto the etching action and attached to the surface of the silicon waferwas counted using a magnifier. The plasma etching was performed usingfluorine-based plasma under the following conditions:

Atmosphere gas: CHF₃:Ar:O₂=80:160:100 mL/minRF power: 1300 W

Pressure: 4 Pa Temperature: 60° C.

Etching time: 50 hours.

The plasma etching test was conducted in the same manner, except forreplacing the atmosphere gas CHF₃ with HCl to create chlorine-basedplasma.

TABLE 3 Number of Particles F-based Plasma Cl-based Plasma Example 1 1623 Comparative 203 289 Example 1

The above results prove that the coating material of the inventionprovides an yttrium oxyfluoride coating having a specifically highhardness and excellent resistance to corrosion by plasma.

INDUSTRIAL APPLICABILITY

The coating material of the invention forms a coating by PVD that ishard and excellent in resistance to corrosion by plasma, such asfluorine-based or chlorine-based plasma. The coating of the inventionexhibits excellent resistance to corrosion by plasma, such asfluorine-based or chlorine-based plasma.

1. A coating material comprising an oxyfluoride of yttrium and having aFisher diameter of 1.0 to 10 μm and a tap density TD to apparent densityAD ratio, TD/AD, of 1.6 to 3.5.
 2. The coating material according toclaim 1, having a pore volume of pores with a diameter of 100 μm orsmaller of 1.0 cm³/g or less as measured by mercury intrusionporosimetry.
 3. The coating material according to claim 1 or 2, havingan angle of repose of 40° or greater.
 4. A coating comprising anoxyfluoride of yttrium and having a Vickers hardness of 200 HV0.01 orhigher.
 5. The coating according to claim 4, having a fracture toughnessof 1.0×10² Pa·m^(1/2) or higher.
 6. The coating according to claim 4,having not greater than 10 projections per 1.0 cm×1.0 cm area thereof.7. The coating according to claim 4, having a thickness of 3 μm orlarger.
 8. A method for forming the coating according to claim 4,comprising forming a coating by physical vapor deposition using acoating material comprising an oxyfluoride of yttrium and having aFisher diameter of 1.0 to 10 μm and a tap density TD to apparent densityAD ratio, TD/AD, of 1.6 to 3.5.
 9. The method according to claim 8,comprising using coating material having a pore volume of pores having adiameter of 100 μm or smaller of 1.0 cm³/g or less as measured bymercury intrusion porosimetry.
 10. The method according to claim 8,comprising using the coating material having an angle of repose of 40°or greater.
 11. The method according to claim 8, wherein the physicalvapor deposition is ion plating.
 12. Use of a powder as a coatingmaterial, the powder comprising an oxyfluoride of yttrium and having aFisher diameter of 1.0 to 10 μm and a tap density TD to apparent densityAD ratio, TD/AD, of 1.6 to 3.5.
 13. The coating material according toclaim 2, having an angle of repose of 40° or greater.
 14. The coatingaccording to claim 5, having not greater than 10 projections per 1.0cm×1.0 cm area thereof.
 15. The coating according to claim 5, having athickness of 3 μm or larger.
 16. The coating according to claim 5,having a thickness of 3 μm or larger.
 17. A method for forming thecoating according to claim 5, comprising forming a coating by physicalvapor deposition using a coating material comprising an oxyfluoride ofyttrium and having a Fisher diameter of 1.0 to 10 μm and a tap densityTD to apparent density AD ratio, TD/AD, of 1.6 to 3.5.
 18. A method forforming the coating according to claim 6, comprising forming a coatingby physical vapor deposition using a coating material comprising anoxyfluoride of yttrium and having a Fisher diameter of 1.0 to 10 μm anda tap density TD to apparent density AD ratio, TD/AD, of 1.6 to 3.5. 19.A method for forming the coating according to claim 7, comprisingforming a coating by physical vapor deposition using a coating materialcomprising an oxyfluoride of yttrium and having a Fisher diameter of 1.0to 10 μm and a tap density TD to apparent density AD ratio, TD/AD, of1.6 to 3.5.
 20. The method according to claim 9, comprising using thecoating material having an angle of repose of 40° or greater.